Manufacture of gasoline and fuel oil



Aug. 29, 1939.

.1. J. powNEY ET A1.

MANUFACTURE OF GASOLINE AND FUEL OIL Filed June l5, 1937 @www N Sw MR HQ@ Aw@ Patented Aug. 29, 1939 UNITED STATES PATENT OFFICE.

MAN UFACTURE OF GASOLINE AND FUEL OIL l corporation of Maine Application June 15, 1937, Serial No. 148,272

8 Claims.

In the processing of crude petroleum stocks to produce lubricating oils, the requirements of the lubricating oil products govern the processing for the simple reason that the lubricating oil products are more valuable than other products produced as a result of such processing. When crude petroleum stocks not useful or not required for the production of lubricating oils are processed for the production of motor fuel gasoline, residual Values are recovered either as coke or, more commonly, as fuel oil. Gasoline being more valuable than fuel oil, such processing has for the most part been governed by the requirements of gasoline production. When such processing, as applied to the particular crude petroleum stocks to be processed, has converted such stocks predominantly into gasoline, such determination of the conditions of processing has not generally been economically satisfactory. However, as applied to crude petroleum stocks of a character such that the value of the fuel oil product, the principal product other than gasoline, becomes substantial with respect to the value of the gasoline product, such determination of the conditions of processing is not economically satisfactory. Specifically, if the value of the fuel oil product is unimportant with respect to the value of the gasoline productl in any particular instance, the quality of the fuel oil product is of correspondingly minor im* portance, but if the proportion of fuel oil produced is so large with respect to the proportion of gasoline produced that the value of the fuel oil product becomes important with respect to the value of the gasoline produced, notwithstanding the greater value of gasoline as compared to fuel oil per unit quantity, then the quality of the fuel oil product, through its effect upon the value of the total production of fuel oil may, and frequently does, limit the economic value of the over-all processing or even render the over-all processing uneconomic. The processing of the more generally available California crude petroleums and reduced crude petroleums, from which lower boiling fractions have been separated by distillation, for the production of gasoline and fuel oil illustrates the situation in which the quality of the fuel oil is a major factor in determining the economic merit of the over-all processing. Any decrease in the ratio of available crude petroleum stocks to gasoline requirements tends` to increase the significance of this factor.

This invention relates to improvements in the manufacture of gasoline and fuel oil from crude petroleum stocks, either not useful or not required for the production of lubricating oils, and more particularly from asphaltic petroleum stocks containing a high boiling wax bearing fraction such as those generally occurring in California.

Motor fuel gasoline must meet definite and established requirements as to volatility and should have good anti-knock value. Several methods of processing crude petroleum stocks to convert substantial portions of them into motor fuel gasoline, by cracking, have been devised and a number of them have been brought to a high state of efficiency with respect to the production of gasoline. Fuel oil must remain fluid and must be sufficiently fluid to permit handling under the conditions prevailing, or which normally `might be encountered, in connection with the use for which it is intended and, for most purposes, it must be so free from sediment thatv it will not tend, in any serious measure, to choke or plug lines, valves, pumps, and burners, and the parts through which it must flow from storage receptacles. In fuel oil specifications, these requirements, appear as a maximum viscosity limitation, as a maximum sediment` content, and as a maximum pour, a maximum temperature below which the oil ceases to flow freely.

Fuel oil specifications also commonly include a minimum gravity, that is a maximum specific Weigh-t, limitation although this limitation is more an arbitrary reiiection of the experience of the fuel oil users with respect to other qualities than any `fundamental quality to which it directly relates. I n the processing of California crude petroleum stocks for the production of gasoline and fuel oil, for example, it isV generally assumed that a satisfactory fuel oil should have a gravity of 10 A. P. I. as a minimum. This assumption apparently is based upon observation that the methods of processing hitherto generally used produced fuel oils which were` too dirty, that is which contained too much sediment, if carried far enough to produce a heavier product.

Residual stocks produced from crude petroleum stocks tend to have a viscosity and a pour too high to be satisfactory as fuel oil. Decomposition at elevated temperatures, and usually under pressure, will reduce the viscosity and the pour of such stocks, but as ordinarily practiced such decomposition, sometimes called viscosity breaking, tends to increase the sediment content of the residual stock, and this tendency increases as the severity of the decomposition necessary to effect the required reduction in viscosity or pour increases. Or, the viscosity and the pour of such stocks may be reduced by leaving in the residual stock, or by blending with it, distillate stocks such as gas oil, but such gas oil stocks are usually more valuable than the residual stock, particularly as raw material for the production of gasoline by cracking. As a consequence the refiner of such crude petroleum stocks has as alternatives the production of a satisfactory fuel oil including fractions potentially more valuable for gasoline production and processing to secure a maximum recovery of gasoline with accompanying production of low quality and consequently low value if not unmercharitable fuel oil. Neither alternative meets the economic requirements of such a rener and, as the ratio between available crude petroleum stocks and gasoline requirements diminishes, the renner in this position is subjected to increasing economic diiculties.

This invention enables the rener processing crude petroleum stocks to produce gasoline and fuel oil to increase the recovery of gasoline without prejudice to the quality of the residual fuel oil produced, or conversely to improve the quality of the fuel oil produced without prejudice to gasoline recovery, and this is one of the more important advantages of the invention. This advantage is, moreover, obtained without sacrice of efciency or economy, but actually with improvements in both efficiency and economy in several respects.

'Ihis invention provides a combined operation in which gasoline is produced in a cracking step to which only clean distillate oil is supplied and in which conditions appropriate to avoid carbon formation are maintained, in which decomposition of residual Stocks appropriate to produce fuel oil at required viscosity and pour is effected without carbon formation by heat exchange with the hot oil products from the cracking` step for a controlled period, in which a maximum of clean distillate stock to be supplied to the cracking step is separated from this residual stock following this controlled decomposition under conditions avoiding further decomposition, and in which stocks relatively more valuable for cracking to produce gasoline are separated from stocks relatively more valuable for blending with residual stocks to produce fuel oil, these separated stocks then being used each for the purpose to which it is best adapted. The invention comprises the combined operation and improvements in various steps of the combined operation and improvements in the adaptation of the combined operation to particular residual stocks presenting specific processing problems.

In one form of operation embodying this invention, a stream of distillate oil is heated to a high cracking temperature under superatmospheric pressure, the hot oil products of this heating and the residual stock to be processed are introduced into a vapor separating receptacle in which they are in direct heat exchanging relationship, a vapor mixture, including the gasoline product and gas oil, and a residual stock mixture are taken oif from this vapor separating receptacle, a high boiling gas oil is vaporized from this residual stock mixture by its contained heat in an evaporator maintained under a pressure lower than that maintained in the vapor separating receptacle, this gas oil, as a vapor mixture, and a reduced residual stock mixture are taken oif from this evaporator, the vapor mixture taken off from the vapor separating receptacle is fractionated to form a gasoline fraction, a high boiling gas oil and a separate lower boiling gas oil, the high boiling gas oil from this fractionation and that taken off from the evaporator are combined and supplied to the heating first-mentioned, and the lower boiling gas oil from this fractionation is blended with the reduced residual stock from the evaporator to form fuel oil.

The accompanying drawing illustrates diagrammatically, generally in elevation one form of apparatus adapted for practicing this invention. In the apparatus illustrated in the drawing, the form of operation just described is carried out as follows: A stream of distillate oil, supplied through connection lll, forced through the heater i by means of pump l' and discharged through connection i9, is heated in the heater l to a cracking temperature upwards of 900 F. under a pressure of from 300 to 800 pounds per square inch gauge, as discharged, for example. After passing through the pressure regulating and reducing valve 2i, the hot oil products discharged from the heater l enter the lower part of the vapor separating receptacle 2 into the upper part of which the crude petroleum stock to be processed is introduced through connection 22 by means of pump 8. A vapor mixture including gasoline and gas oil is taken off from the upper end of the vapor separating receptacle 2 through connection 23 and introduced into the lower part of the fractionating tower ll, and the residual stock mixture separated in the vapor separating receptacle 2, including residual components of the hot oil products discharged from the heater as well as residual components of the stock introduced through connection 22, is discharged through the pressure regulating and reducing valve 25 and connection 2li into the evaporator 3. A pressure of from 20 to 60 pounds per square inch for example, may be maintained in the vapor separating receptacle 2. A vacuum of from 10 to 25 inches of mercury, for example, may be maintained in the evaporator 3, by means of the exhauster 3i operating in conjunction with pumps ii and l2. A high boiling gas oil is vaporized in the evaporator 3 and, passing to the heat exchangers 32 and 33 through connection 3Q., is condensed, the condensate being collected in receiver 35. Except for that part introduced into the upper end of the evaporator 3 through connection 36 by means of pump l2, this condensed high boiling gas oil is introduced into the lower part of the fractionating tower d through connection l2 by means of pump l2. The fractionating tower l separates the stocks introduced through connections 23 and 42 into a gasoline fraction discharged through connection 53, a high boiling gas oil supplied to the heater l through connection d! and a low boiling gas oil taken off as a side stream through the stripper 4d and connection 45. Except for that part returned to the fractionating tower 4 through the absorber 5, this lower boiling gas oil is discharged through connection !56. The reduced residual stock mixture separated in the evaporator 3 is 'discharged through connection 3l by means of pump El. The gasoline product is separated from the vapor mixture discharged from the fractionating tower l through connections 43 and 38, in any convenient manner, such as by the processing subsequently described. The fuel oil product is produced by blending the reduced residual stock discharged through connection 3i' and the lower boiling gas oil discharged through connection 36.

The heating, in which the stream of distillate oil is heated to a high cracking temperature under superatmospheric pressure, the heating carried out in the heater I in the apparatus illustrated, for example, is, in the combined operation of this invention so controlled with respect to temperature, temperature gradient, pressure and time as to prevent substantial formation of carbon or sediment, during this stepy of the operation. The correlation of these several factors to this end and various forms of heating apparatus for maintaining such correlation, as applied to the processing of a clean distillate stock, are well known. The particular form of apparatus and the particular technique may be chosen in any particular instance, to meet the requirements of the particular reflner. In general, however, it is advantageous, in the combined operation of this invention, to avoid substantial digestion, or soaking of the hot oil products ilowing through and ldischarged from this heating step prior to introduction into the vapor separating receptacle. That is, in the combined operationof the invention it is advantageous to have the temperature of the oil progressively increased as it flows through the heating step and to avoid conditions which tend. to maintain the flowing oil prior to discharge into the vapor separating receptacle at approximately the Same temperature forv any prolonged period of time. Such digestion tends to increase the. sediment content of the fuel oil produced by the combined operation. The conditions in the vapor separating receptacle are so controlled that no substantial carbon formation takes place therein. A temperature, and a pressure, suincient to eifect a reduction of the viscosity of residual components of the introduced residual stock while passing therethrough may, however, he maintained therein with advantage. For example, a maximum temperature approximating SZW-840 F., and the corresponding pressure may be maintained in this externally unheated vapor separating receptacle while maintaining therein a liquid body equivalent in volume to about 8-10 minutes discharge of residual stock mixture therefrom. The conditions in the evaporator, into which the residual stock mixture separated in the vapor separating receptacle is discharged, are so controlled that no substantial decomposition takes place therein.

As applied to an asphaltic petroleum stock containing a high boiling wax bearing fraction, a California crude petroleum or reduced crude petroleum of this character for example, the high boiling wax bearing fraction of the crude petroleum stock is` taken off from the vapor separating receptacle into which this crude petroleum stock is introduced as a component of the residual stock mixture separated in the vapor separating receptacle and is then vaporized from this residual stock mixture Without substantial decomposition in the evaporator. In the vapor separating receptacle, conditions of temperature and pressure appropriate to effect a reduction of the viscosity of residual components of the introduced crude petroleum stock but without substantial formation of carbon or sediment, are with advantage maintained. Then, in the evaporator, further decomposition. which would tend to increase the sediment content of the reduced residual stock is avoided by effecting this step of the operation under a lower pressure and under a correspondingly lower temperature and by effecting this vaporization by the contained heat of the oil, through this pressure reduction, rather than by the application of external heat to the evaporator. A reduction of the pour of the reduced residual stock is eiected by the separation, in the evaporator, of the high boiling wax bearing fraction. The high boiling wax bearing fraction separated in the evaporator, a high boiling gas oil, is then condensed and supplied, as a clean distillate oil, to the heating in which it is cracked for the production of gasoline. The clean distillate oil supplied to the cracking for the production of gasoline also comprises, with advantage, the high boiling gas oil condensed from the vapor mixture taken off from the vapor separating receptacle. This vapor mixture taken oiffrorn the vapor separating receptacle is, with advantage, fractionated to form a gasoline fraction, a high boiling gas oil and a separate lower boiling gas oil. Such high boiling gas oil is a desirable stock, or stock component, for cracking to produce gasoline. Such lower boiling gas oil is less desirable as a Stock for cracking to produce gasoline, being relatively refractory and tending to reduce the capacity of the cracking step if supplied thereto in admixture with the higher boiling gas oils taken off from the` vapor separating receptacle and the evaporator, but it is substantially free from wax and is very effective, as a diluent, in reducing the viscosity of residual stocks With which it is blended and is, with advantage, blended with the reduced residual stock separated in the evaporator to produce fuel oil of improved viscosity and pour.

The invention will be further illustrated by the following specific example of one operation embodying the invention as practiced in apparatus of form illustrated in the accompanying drawing: A stream of clean distillate oil is forced through the heater i by means of pump 'l at a rate of about 12,050 gallons per hour and at a temperature, entering the heater, of about 610 F., and in the heater it is progressively heated to a temperature of about 940 F. under a pressure, as discharged from the heater, approximating 400 pounds per square inch. The heater may consist, for example, of two banks of tubes 3" in inside diameter, '74 tubes exposed over 32 feet of their length being serially connected in each bank and the two banks being connected in parallel. The pressure on the stream of hot oil products discharged from the heater is reduced to about 55-60 pounds per square inch as it passes through the valve 2i through which it enters the vapor separating receptacle 2. In addition to the hot oil products discharged into the vapor separating receptacle 2 from the cracking heater I, reduced California crude petroleum is introduced into the vapor separating receptacle 2 through connection 22 by means of pump 8 at a rate of about 4,830 gallons per hour and at a temperature, entering the vapor separating receptacle, approximating 415 li. After leaving the pump 8, the reduced crude petroleum flows first through the heat exchanger 32 and then through the heat exchanger lill, being thus preheated to this temperature. Temperatures of about 735 F. and 825 F. are maintained in the upper and lower ends respectively, of the vapor separating receptacle 2. A vapor mixture is taken off from the vapor separating receptacle through connection 23, through which it is discharged into the fractionating tower 6., at a rate of about 13,- 035 gallons per hour and a reduced residual stock is discharged from vapor separating receptacle 2 through connection 24 at a rate of about 3,995 gallons per hour. A volume of liquid residue approximating 570 gallons is` maintained in the lower end of the vapor separating receptacle. A subatmospheric pressure corresponding to about le" of mercury is maintained in the receiver 35 by means or" the exhauster 3l. This receiver 35 is in free communication with the evaporator 3 through connection 34 and a corresponding subatmospheric pressure is thus maintained in the evaporator. The pressure on the residual stockl discharged from the vapor separating receptacle 2 is reduced as it passes through valve 25 to enter the evaporator. Under these conditions, the contained heat of the residual stock mixture discharged from the vapor separating receptacle at a temperature approximating 825 F. is suicient to maintain, in conjunction with the refluxing subsequently described, temperatures of about 710 F. and 730 F. in the upper and lower ends respectively, of the evaporator 3. The reduced residual stock mixture, tar, is pumped, by means of pump il, from the lower end of the evaporator at a rate of about 2,470 gallons per hour. The vapor mixture separated in the evaporator 3 is taken on through connection 34 at a rate of about 1,525 gallons per hour, this vapor mixture being condensed and cooled to a temperature of 220 F. as it passes through the heat exchangers 32 and 53. About 155 gallons per hour of this condensate is reintroduced into the evaporator through connection 36 and the balance, about 1,370 gallons per hour, is pumped into the fractionating tower 4 through connection 42 by means of pump- I2. The fractionating tower 4 is maintained under a pressure of about 30-40 pounds per square inch and temperatures of about 365- 370" F. and 625 F. are maintained at the upper and lower ends respectively, of this ractionating tower by appropriate reluxing. The gasoline fraction including the gas produced in the operation is discharged from the fractionating tower i through connection 43 at a rate of about 5,650 gallons per hour. A lower boiling gas oil, an intermediate fraction, is taken oii from the fractionating tower as a side stream through the stripper 44 and a high boiling gas oil is collected in the lower end of the fractionating tower 4. Stocks subjected to fractionation in the fractionating tower include the several stocks or stock mixtures introduced through connection 42 as well as the stock introduced as a Vapor mixture through connection 23. Appropriate reluxing is effected by condensing a part of the vapor mixture discharged from the fractionating tower through connection 433, in condenser 39 discharging into receiver All, and reintroducing this condensate into the upper end of the fractionating tower through connection by means of pump I5 at a rate of about 2,960 gallons per hour and at a temperature approximating -90 F. Refluxing by circulation of any appropriate cooling medium through the heat exchanger 49 may be used in place of or as a supplement to such reiiuxing by reintroduction of a condensed portion of the discharged vapor mixture. A part of the lower boiling gas oil taken oi through the stripper M is circulated through the absorber -5 and back to the fractionating tower 4, through connection A52 by means of pump I1. This part of the lower boiiing gas oil is used as an absorbent in the absorber 5 to recover gasoline -constituents from the gas mixture separated from `the gasoline condensate in receivers 47 and 5I, the absorbed gasoline constituents being vaporized from the absorbent upon reintroduction of the absorbent into the fractionating tower 4. The balance of the lower boiling gas oil taken off through the stripper 44, about 830 gallons per hour, is discharged through connection 55. A part, about 8,590 gallons per hour, of the high boiling gas oil accumulating in the lower end of the fractionating tower t at a temperature approximating 625 F. is used as a heating medium in the operation of the stabilizer 5 and in p-reheating in heat exchanger ll the reduced crude petroleum to be introduced into the vapor separating receptacle 2. That part of this high boiling gas oil used in the operation of the stabilizer, about 1,310 gallons per hour, is circulated through the heat exchanger or reboiler 5l by means of pump I3 and that part used in preheating the reduced crude petroleum is circulated through the heat exchanger 35 by means of this same pump i3, the oil returning from lthe heat exchangers 45 and 5I being reintroduced into the fractionating tower l through connection 52. "in addition to the high boiling gas oil from the receiver 35, the low boiling gas oil charged with absorbed gasoline constituents from the absorber 5 and the circulated gas oil returned from heat exchangers d@ and 5I, virgin gas oil of a gravity approximating SSR-34 A. P. I. is pumped into the fractionating tower d through connection t2 by means of pump 9 at a rate of about 950 gallons per hour. The clean distillate stock supplied to the cracking heater I is the composite high boiling gas oil character stock separated in the lower end of the fractionating tower and is supplied to the pump 'I delivering to the cracking heater I through connection lil. That part of the vapor mixture discharged from the fractionating tower 4 through connection i3 not delivered to the condenser 39 is delivered to the condenser 50 discharging into the receiver 5I. The bulk of the gasoline content of this part of the vapor mixture is condensed in the condenser 50 and is separated from gases and uncondensed vapors in the receiver 5I. 'Ihe mixture of gases and uncondensed vapors separated in the receivers 41 and 5I is discharged into the absorber 5 through connection 52 for recovery of gasoline constituents as previously described. The absorbent oil supplied to the absorber 5 is cooled, in the heat exchanger 53, to a temperature of about 80 F. before being introduced into the upper end of the absorber through connection 54. A pressure of about 30 pounds per square inch is maintained in the receiver 5I, and in the receiver 131, to promote the separation of condensable constituents from the gas mixture in these receivers. A pressure of about 28 pounds per square inch is maintained in the absorber 5. The gasoline condensate separated in the receiver 5I is pumped, by means of pump I6, through connections 52 and 63 and heat exchanger 6l! into the stabilizer 5 in which this gasoline condensate is accurately fractionated at the lower end of its boiling range to produce a gasoline product discharged from the lower end of the stabilizer 6 through heat exchanger Bil, cooler 65 and connection 66 at a rate of about 2,120 gallons per hour. Stabilizer '5 is operated under a pressure, at the upper end, of about 250-260 pounds per square inch. A temperature of about 380- 385 F. is maintained at the lower end of stabilizer 6 by means of heat supplied through heat exchanger I. A temperature of about F. is maintained at the upper end of stabilizer 5 by reintroducing condensate condensed and separated from the gas mixture escaping from the upper end of the stabilizer through connection Si, in condenser 68 and receiver GQ, through connection "I5 by means of pump I8. Dry gas is rating receptacle.

discharged from the upper end of the absorber through connection 55 at a rate of about 31,600 cubic feet per hour and dry gas is discharged from receiver B9 through connection 'Il at rate of about 1,500 cubic feet per hour.

In one operation conducted as just described, in apparatus of the form illustrated in the accompanying drawing, supplying California reduced crude petroleum having a gravity of 17.3 A. P. I. and virgin gas oil from California lcrude petroleum having a gravity of 33.8 A. P. I., a tar separated as a reduced residual stock in the evaporator 3 having a gravity of 4.9 A. P. I., a low boiling gas oil having a gravity of 26.9 A. P. I. and a gasoline having a gravity of 57.7 A. P. I. were produced. This gasoline `product had an octane value of 69.5 and a vapor pressure of 10.4 pounds per square inch. This tar, as discharged from the evaporator, had a Furol viscosity at 210 F. of 163 seconds, a pour of 100 F. and a content of sediment by extraction with benzol of 0.06%. The low boiling gas oil produced was available for blending with this tar in proportions exceeding 20% of the blended fuel oil product. In blends comprising and 20% of such gas oil, the Furol viscosities at 210 F. of the blends were 46 seconds and 22 seconds respectively, the pours of the blends were 75 F. and 40 F. respectively, and the sediment contents by extraction with benzol were 0.04% and 0.03% respectively.

The combined operation, as carried out in apparatus of the form illustrated in the accompanying drawing, is conveniently controlled by reference to the heat balance in the vapor sepal With hot oil products discharged from the cracking heater into the vapor separating receptacle at a given rate and at a given temperature, the rate at which a residual stock can be introduced into the vapor separating receptacle is governed by the temperature at which this residual stock is introduced, the permissible rate of introduction of the residual stock increasing and decreasing respectively, with increase or decrease of the temperature at which the residual stock enters the vapor separating receptacle. If this relationship is adjusted to permit the introduction of the residual stock at a rate suiiicient toproduce the total clean distillate oil, including the high boiling gas oil taken off from the vapor separating receptacle and the high boiling gas oil taken off from the evaporator, required to supply the cracking heater, additional stock need not be supplied to meet the requirements of the heater. However, the temperature at which the residual stock is introduced into the vapor separating receptacle must also be so related to the rate at which it is introduced into the vapor separating receptacle, and with respect to the rate at which heat is supplied to the vapor separating receptacle in the hot oil products discharged from the cracking heater, that conditions, and particularly the temperature, inthe vapor separating receptacle, do not reach a point at which decomposition involving the formation of carbon or an increase in the sediment content of the residual stock mixture Separated therein becomes substantial. In general, this means that the temperature of the residual stock as introduced into the vapor separating receptacle must not be too high. An operating balance will be found, in any particular instance, between the limits fixed by these two requirements, namely, the avoidance of objectionable decomposition in the vapor separating receptacle and the production of sufficient clean distillate oil to supply the cracking heater, any variation being made up by a supplementary supply of a clean distillate oil from some external source. The particular method used for preheating the crude petroleum stock introduced into the vapor separating receptacle is not essential tothis invention. If it be nre-heated, however, it must not be so heated to a temperature at which objectionable decomposition begins. In the apparatus illustrated in the accompanying drawing, for example, after leaving the pump 8, the crude petroleum stock may flow in whole or in part through the heat exchanger 32 and in whole `or in part through the heat exchanger 40, the several valves 8i, 82, 83, 84, 85, 86 and 81 being provided for distribution and regulation of this flow. i

Several advantages of the invention will be apparent from the foregoing. In the combined operation of the invention the cracking to produce gasoline is separated from the decomposition to `reduce the viscosity, and pour, of the fuel oil in respects which permit eiective cracking of an increased proportion of the stock supplied to the combined operation after separation as a clean distillate oil while avoiding over-decomposition alike of the clean distillate oil and the separated residual components tending to produce dirty fuel oil although this cracking and decomposition are combined in respects which utilize the heat content of the hot oil products discharged from the cracking operation to effect the decomposition of the residual components of the stock supplied to the combined operation in` a particularly advantageous manner and which enable the residual components produced by the cracking of the clean distillate oil to be used with maximum effect in reducing the viscosity, and pour, of the composite residual stock mixture produced by the operation, without contamination of the residual stock mixture with carbon or sediment. The residual components of the stock supplied to the combined operation are subjected to decomposition under mild conditions and increased proportion of the stock supplied to the combined operation is separated as a clean distillate oil and as such is subjected to eifective cracking to produce gasoline, thus permitting a more effective cracking to produce gasoline of an increased proportion of the total stock supplied to the combined operation without involving overcracking or over-decomposition of any part of the total stock. Also, the higher boiling gas oil separated in the fractionating step of the combined operation of the invention is more desirable as a stock for cracking to produce gasoline than the lower boiling gas oil separated in this fractionation and in the combined operation this more desirable cracking stock is subjected to effective cracking while the lower boiling gas oil, relatively refractory and less desirable as a cracking stock but more effective as a diluent for blending with the reduced residual stock mixture separated in the evaporator for the production of fuel oil is made available for such blending.

The term cracking is used herein to refer to pyrolysis to produce gasoline as distinguished from pyrolysis limited in eiect to the reduction of viscosity, or pour, and not with that broader meaning with which it is sometimes used to include pyrolysis generally. In referring to a high cracking temperature herein reference is intended to cracking temperatures ranging upwards #from 900 F. to about 975 F.985 F., for example. The term carbon is use-d herein to include those solid or semi-solid materials, carbon-like or coke-like, which are produced by pyrolysis and is not intended to be limited to carbon in the strict chemical sense. Reference to Wax bearing stocks herein is not intended as a reference to stocks necessarily obtaining any large proportion of wax. The presence of determinable quantities of Wax, by low temperature extraction with ether and absolute alcohol of the distillate obtained on running a sample to coke, even though in but fractions of a per cent, in crude petroleum stocks tends to involve difculties of the sort with which this invention deals. The term crude petroleum stocks is intended to include both crude petroleum as such and reduced crude petroleum. Over-cracking or over-decomposition as those terms `are used herein can be recognized by extraction with benzol of the residual product of the cracking or decomposition, objectionable over-cracking or overdecomposition usually being indicated by a sediment content on such extraction with benzol of as much as one tenth of one per cent or more.

The unusual cleanliness of the tar recovered as a reduced residual stock mixture from the evaporator in combined operation of this invention makes it available not only for the production of fuel oil but also for the production of road oil and, with appropriate blowing, of asphalt. Such reduced residual stocks can be regularly produced by the combined operation of this invention, with sediment contents, by extraction with carbon bisulphide and carbon tetrachloride, of substantially less than one tenth or two tenths of one per cent. It is thus possible, by separating sucient distillable material from the reduced residual stock mixture in the evaporator to produce merchantable road oil as a direct product of the combined operation. The same properties which make this reduced residual stock mixture desirable as road oil also make it desirable as a stock to be processed for the production of asphalt.

We claim:

1. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradient, pressure and time during said heating to prevent'substantal formation of carbon therein, reducing the pressure on the hot oil products of said heating and bringing them into direct heat exchanging relationship with the asphaltic stock containing the high boiling wax bearing fraction in a vapor separating receptacle without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, taking off from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a vapor mixture including gas oil and gasoline; vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling wax bearing fraction and supplying it to said heating.

2. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, Vthe improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradient, pressure and time during said heating to prevent substantial formation of carbon therein, reducing the pressure on the hot oil products of said heating and bringing theminto direct heat exchanging relationship with the asphaltic stock containing the high boiling Wax bearing fraction in a vapor separating receptacle without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, taking off from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a vapor mixture including gas oil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling wax bearing fraction and supplying it to said heating, together with gas oil condensed from said vapor mixture.

3. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing ahigh boling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradient, pressure and time during said `keating to prevent substantial formation of carbon therein, bringing the hot oil products of said heating into direct heat exchanging relationship with the asphaltic stock containing the high boiling wax bearing fraction in a vapor separating receptacle Without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, taking off from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a Vapor mixture including gas oil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture Without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, condensing this high boiling Wax bearing fraction to form a high boiling gas oil, fractionating said vapor mixture to form a gasoline fraction, a high boiling gas oil, and a separate lower boiling gas oil, and combining and supplying to said heating said high boiling gas oils.

4. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradient, pressure and time during said heating to prevent substantial formation of carbon therein, bringing the hot oil products of said heating into direct heat exchanging relationship with the asphaltic stock containing the high boiling Wax bearing fraction in a vapor separating receptacle Without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, taking 01T from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a Vapor mixture including gas oil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a. pressure lower than that maintained in said receptacle, condensing this high boiling wax bearing fraction to form a high boiling gas oil, fractionating said vapor mixture to form a gasoline fraction, a high boiling gas oil, and a separate lower boiling gas oil, and combining and supplying to said heating said high boiling gas oils, and blending said lower boiling gas oil With residual stock from said evaporator to form fuel oil.

5. In the manufacture of gasolin-e and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure without substantial digestion, bringing the hot oil products of said heating into direct heat exchanging relationship with the asphaltic stock containing the high boiling wax bearing fraction in a vapor separating receptacle without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, maintaining a temperature and pressure in said vapor separating receptacle suiicient t0 effect a reduction of the viscosity of residual components of said asphaltic stock but without substantial formation of carbon therein, taking off from said receptacle a resi-dual stock mixture including the high boiling wax bearing fraction and a vapor mixture including gas oil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling wax bearing fraction and supplying it to said heating.

6. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure without substantial digestion, bringing the hot oil products of said heating into direct heat exchanging relationship with the asphaltic stock containing the high boiling wax bearing fraction in a Vapor separating receptacle without prior heating' of said asphaltic stock to a temperature at which substantial decomposition occurs, maintaining a temperature and pressure in said vapor separating receptacle suicient to effect a reduction. of the viscosity of residual components of said asphaltic stock but without substantial formation of carbon therein, taking off from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a vapor mixture including gasoil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling' wax bearing fraction and supplying it to said heating, together with gas oil condensed from said vapor mixture.

7. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradi-ent, pressure and time during said heating to prevent substantial formation of carbon therein, introducing the hot oil products of said heating into an externally unheated vapor separating receptacle and therein bringing said hot oil products into direct heat exchanging r-elation with the asphaltic stock' containing the high boiling wax bearing fraction Without prior heating of said asphaltic stock to a temperature at which substantial decomposition occurs, maintaining in said receptacle a maximum temperature approximating 820 F.-840 F. and maintaining therein a liquid body equivalent in volume to about 8-10 minutes discharge of residual stock mixture therefrom, whereby the viscosity of the residual components of the asphaltic stock introduced into said receptacle is reduced, taking off from said receptacle a residual stock mixture including the high boiling wax bearing fraction and a vapor mixture including gas oil and gasoline, vaporizing the high boiling wax bearing fraction from this residual stock mixture without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling Wax bearing fraction and supplying it to said heating.

8. In the manufacture of gasoline and fuel oil from asphaltic petroleum stocks containing a high boiling wax bearing fraction of the type generally occurring in California, the improvement which comprises heating a stream of distillate oil to a high cracking temperature under superatmospheric pressure and controlling the temperature, temperature gradient, pressure and time during said heating to prevent substantial formation of carbon therein, reducing the pressure on the hot oil products of said heating and introducing them into an externally unheated vapor separating receptacle and therein bringing said hot oil products into direct heat exchanging relationV with the asphaltic stock containing the high boiling wax bearing fraction without prior heating of said asphaltic stock tot a temperature at which substantial decomposition occurs, maintaining a temperature and a pressure in said vapor separating receptacle suiiicient to effect a reduction of the viscosity of residual components of said asphaltic stock but without substantial formation of carbon therein, taking off from sai-d receptacle a residual stock' mixture including thehigh boiling wax bearing fraction and a vapor mixture including gas oil and gasoline, Vaporizing the high boiling wax bearing fraction from this residual stock mixture Without substantial decomposition by the contained heat of the oil in an evaporator maintained under a pressure lower than that maintained in said receptacle, and condensing this high boiling wax bearing fraction and supplying it to said heating.

JOHN JOSEPH DOWNEY. WILLIAM WALLACE MURRAY. 

